System including a hard disk drive and stray magnetic field sensor and associated method

ABSTRACT

A system includes a host device and a disk drive interfaced with the host device are described as well as an associated method. The disk drive includes a magnetic media for storing information using an actuator arrangement to perform a data access by moving at least one head proximate to the magnetic media. The information may be subject to corruption when the disk drive is exposed, during the data access, to a given stray magnetic field having a given minimum magnetic field intensity. The given stray magnetic field will not corrupt the information on the magnetic media with the actuator arrangement positioned away from the magnetic media. A stray magnetic field protection arrangement is configured for detecting an ambient magnetic environment for use in causing the actuator arrangement to park responsive to the detection of at least the given minimum magnetic field intensity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 11/327,765 filed on Jan. 6, 2006, which is incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

Hard disk drives, as well as other forms of storage devices, which store information in magnetic form, are susceptible to external magnetic fields. Accordingly, subjecting a hard disk drive, or other such device using magnetic based storage, to an externally generated magnetic field can produce defects that prevent a user from retrieving data therefrom. Although the following discussion may be adapted for use with other forms of storage devices, it is framed in terms of a hard disk drive in order to clearly illustrate the various concepts that have been brought to light herein.

Thus, there are limitations in the prior art with respect to the operation of a hard disk drive that may be subject to exposure to stray magnetic fields.

The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.

BRIEF SUMMARY OF THE INVENTION

The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other improvements.

A system and associated method are described for use in protecting a disk drive from a hostile magnetic environment. The system includes a host device. A disk drive is interfaced with the host device and includes a magnetic media for storing information, and which information is accessed using an actuator arrangement for performing a data access by moving at least one head proximate to the magnetic media. The information may be subject to corruption when the disk drive is exposed, during the data access, to a given stray magnetic field having a given minimum magnetic field intensity, which given stray magnetic field is generated external to the system. A stray magnetic field protection arrangement is configured for detecting an ambient magnetic environment to which the disk drive is exposed and, responsive thereto, for causing the actuator arrangement to park responsive to the detection of at least the given minimum magnetic field intensity.

In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be illustrative rather than limiting.

FIG. 1 is a block diagram of a host device and hard drive that is housed in the host device, shown here to illustrate the use of a stray field or external magnetic field sensor.

FIG. 2 is a flow diagram showing one embodiment of a technique for monitoring the magnetic sensor that is illustrated in FIG. 1.

FIG. 3 is a flow diagram showing another embodiment of a technique for monitoring the magnetic sensor that is illustrated in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the described embodiments will be readily apparent to those skilled in the art and the generic principles taught herein may be applied to other embodiments. Thus, the present invention is not intended to be limited to the embodiment shown but is to be accorded the widest scope consistent with the principles and features described herein including modifications and equivalents, as defined within the scope of the appended claims. It is noted that the drawings are not to scale and are diagrammatic in nature in a way that is thought to best illustrate features of interest. Descriptive terminology has been adopted for purposes of enhancing the reader's understanding, with respect to the various views provided in the figures, and is in no way intended as being limiting.

Turning now to the drawings, wherein like components are indicated by like reference numbers throughout the various figures, attention is immediately directed to FIG. 1 a, which is a block diagram illustrating an electronic host device, generally indicated by the reference number 10, manufactured in accordance with the present invention. It is to be understood that device 10 is intended to be representative of any number of digitally implemented device types including, but not limited to wireless telephones, internet appliances, personal digital assistants, music players, multi-function pagers, multimedia devices or any other device adaptable to use with an electromechanical digital storage device. The present invention is well suited for use in devices which may, at times, be subjected to use in a “hostile” magnetic environment. Applicant recognizes that portable devices, in particular, can commonly be exposed to such an environment. Such exposure can occur, for example, by placing the portable device into a pouch with a magnetic closure mechanism, exposing the device to magnetic-based security devices, placing the device near magnets, magnetized tools, motors, or electronics, such as a CRT or current-carrying wires, or other environments wherein a magnetic field is found.

The present disclosure, however, is in no way limited to use in portable devices. Further, the teachings herein find application where any appropriate storage device may be subjected, at least briefly, to stray external magnetic fields.

Continuing with a description of FIG. 1, host device 10 includes a processing arrangement 12 configured for operating the overall device. A host memory section 14 is associated with processing arrangement 10 which may be, for example, a suitable form of RAM. Alternatively, the memory section can be made up of a suitable combination of ROM and RAM wherein a volatile RAM portion of the memory section is loaded for device operation during an initial boot-up.

With continuing reference to FIG. 1, device 10 further comprises a user interface arrangement, for example, in the form of a keypad 16, a display 17 and a headset connector 18 that is connected to an external headset 19. Other items include an interface 20 that may be configured in accordance with a number of well-known interface arrangements such as, for example, compact flash, IDE or any other suitable interface that is currently in use or yet to be developed.

A hard drive 30 is housed within host device 10 and includes a connector arrangement 32 that is electrically connected to interface 20, for example, using a flexible connector, as shown having a connection end 34, or any other suitable connection scheme. Hard drive 30 may be of any suitable configuration based, at least in part on considerations with respect to host device 10. In one implementation, for a portable device, a miniature hard drive such as the CORNICE®. Storage Element may be used, although it is to be understood that a hard drive having any suitable form factor may be utilized. Hard drive 30 may be removably received, for example, in a compact flash implementation or mounted as permanent internal storage.

Continuing to refer to FIG. 1, hard disk drive 30 includes a number of functional elements that will be familiar to one having ordinary skill in the art. Among these elements are an actuator 40 configured for selectively moving a transducer arrangement or “head” 42 which accesses a disk arrangement 44. The drive may include any suitable number of disks and heads wherein one or both sides of each disk can be used for data storage purposes. Head 42 is configured to cooperate with the rotation of an associated disk, in disk arrangement 44, so as to “fly” above the surface of the disk, in a well-known manner. A microprocessor 50 is used to control a servo section 52 that is itself configured for controlling disk arrangement 44, using a spindle control section 54, and for controlling actuator 40. Disk data is handled under control of microprocessor 50 using a read/write channel 60 in cooperation with a data interface 62. A memory section 70 contains code for use by microprocessor 50 in operating the overall drive, as will be described in further detail hereinafter.

With the general structure of hard drive 30 in mind, Applicant has recognized a particular phenomenon that appears to occur when drive 30 is exposed to an external magnetic field in a given range of magnetic field strength. While not intending to be bound by theory, it is thought that, in this given range, the shielding and/or write structures in magnetic read/write heads 42 can become magnetized by the stray field, and focus the now concentrated stray field onto the disk, when the heads are accessing the disk (i.e., the heads are loaded). If the stray field is strong enough, as represented by this given range of magnetic field strength, the focused or resulting field from the magnetized structures can demagnetize the data already written on the disk, including critical servo data. In this case, certain data on the disk will become damaged and lost due to magnetic erasure from the stray magnetic field. Since all disk drives use similar head technology, it is thought that all disk drives may be relatively similar in sensitivity to such stray magnetic fields and this now recognized mechanism of data loss. Hence, this given range may be referred to hereinafter as a focusing effect range (FER). In this regard, when a magnetic field exceeding a lower limit of the field effect range is detected at the hard disk drive during operation, it is generally safer to remove the head from the disk surface and park it at least until the magnetic field has reduced to a value that is below the focusing effect range. Applicant believes that the focusing effect described above is significant. That is, the given range in which data damage occurs, responsive to the aforedescribed focusing effect, is believed to be significantly lower than a stray magnetic field strength that would produce data loss even with the head in a parked position. Thus, a margin of safety is afforded by parking the actuator arm and heads whenever the stray field strength crosses the lower threshold limit of the focusing effect range such that data loss and corruption is avoided when the stray field remains at a signal strength that is within the focusing effect range.

In view of the foregoing, and having generally described host device 10 including hard drive 30, housed therein, additional features of the illustrated system include a magnetic sensor 80 that is incorporated into hard disk drive 30, in the present example. A sensor electrical connection 82 is routed to a signal conditioning section 84 and, in turn, to microprocessor 50. It should be appreciated that signal conditioning section 84 may be optional depending upon the configuration of magnetic sensor 80. The latter, in the present example, is a tri-axial sensor or orthogonal arrangement of single axis sensors for sensing along axes x, y and z, so that the ambient magnetic environment can be detected irrespective of its specific orientation in relation to the sensor. Further, the orientation of the ambient stray field can also be determined. It is noted sensors or sensor arrangements capable of sensing along two orthogonal axes or even a single axis can be used, depending, for example, on the desired level of protection and anticipated characteristics of the ambient stray field. Depending on the application, it is possible to make certain pragmatic assumptions about the rate of change of magnetic field that the device is likely to experience. The magnetic field sensor signal should be sampled rapidly enough to avoid damage due to a potentially immediately applied magnetic field. It is generally considered that sampling every 10 ms is adequate for typical applications in portable devices, but slower or faster sampling rates are possible depending on the application. Sensor 80 may be of any suitable type that is responsive to magnetic fields. Such sensors include, but are not limited to Hall effect sensors, magnetoresistive, giant magnetoresistive (GMR), and tunneling junction magnetoresistive sensors, magneto-inductive sensors, magneto-impedance sensors, magneto-optic sensors (Faraday, Kerr effects), search coil, flux-gate magnetometers, Superconducting Quantum Interference Devices (SQUID), spin-resonance magnetometers, magneto-biological sensors, such as alignment of magnetotactic bacteria, photon precession sensors, or nuclear precession (Overhauser effect) sensors, as well as others. More specifically, a Hall effect sensor such as the AD22151 from Analog Devices could be used for single-axis sensing.

It is noted that some sensors, such as, for example, Hall effect and magnetoresistive sensors, are uniaxially oriented devices that are sensitive to a single component of the applied magnetic field vector. Since, in general, the applied field can have any vector orientation, an array of these sensors can be oriented orthogonally to each other in order to measure the orientation of the field, as well as its total vector magnitude.

With continuing reference to FIG. 1, operation of hard drive 30 proceeds based on control code that is stored in memory section 70. The latter includes drive code 90, which is used to control the overall functionality of hard drive 30 including coordinating motion of actuator 40 with rotation of disk arrangement 44 by servo section 52, and sensor code 92 for use in monitoring magnetic sensor 80. Execution of sensor code 92 may occur periodically within the framework of an overall routine which includes executing drive code 90. Of course, the speed of microprocessor 50 may, at least in part, establish how often the sensor code can be executed. As noted above, it is contemplated that the sensor code may be executed at least every 10 ms. In this way, sensor output events having durations on the order of 20 ms or more are readily detectable.

Referring to FIG. 2 in conjunction with FIG. 1, specific details with respect to one embodiment of sensor code 92 will now be provided. The sensor code is entered at a start step 100 following which a sensor output 102 is established. Step 104 then determines whether the sensor output value is greater than a predetermined threshold value that is selected as will be described below to establish whether the stray magnetic field strength is greater than a predetermined threshold value at a particular orientation (which may include any orientation). In this regard, a multi-axial sensor or orthogonal sensor arrangement will detect an incident stray field irrespective of its particular orientation. It is noted that the predetermined threshold should be equal to or less than the lower limit of the focusing effect range. When this condition is detected, step 120 is then initiated so as to immediately park or retract actuator 40 and its associated head 42 or heads. For a hard drive which utilizes an active latching arrangement, any appropriate activities may be performed that are necessary for latching the actuator in its parked position. Further, in order to minimize disruption of ongoing operations, any current data access is paused until such time that normal operations resume. Such a pause is available in data communication protocols over interfaces commonly used for hard disk drives (such as ATA, SCSI, CE-ATA, MMC-ATA) all include standard features which allow data transfer on the interface to be temporarily paused for mechanical related activities such as seeking, retries, error recovery and the like. An indication of the sensor status to the host device can be provided on a sensor status line 124 that is dedicated for that purpose. Further, the host device or the hard drive can support a function wherein a message is visually displayed or otherwise communicated, perhaps audibly, to the user to remove the device from the magnetic field. Any suitable number of such sensor status lines can be used to indicate to the host device a particular one of a number of possible conditions associated with a sensor. The use of one or more dedicated sensor status lines may be advantageous if the triggering event causes drive processor 50 to enter a wait condition such that the drive processor may not otherwise notify the host processor as to the cause of the current pause or wait status. Further, it should be appreciated that the number of sensor status lines can be limited, for example, by multiplexing sensor status information thereon.

It is of note that detecting a mere return of the sensor output to a detected magnetic field strength, that is below the focusing effect range, may be a momentary event. That is, the stray external magnetic field may be varying and have passed through a zero or reduced magnitude phase. Accordingly, step 126 again reads sensor 80, subsequent to the parking operation. At this point, it is generally desirable that actuator 40 remain parked, so long as the sensor continues to exhibit an output that is greater than the predetermined threshold. In consideration of time-varying magnetic fields, step 128 again compares the sensor output to the predetermined threshold and, upon detecting a value that is less than the predetermined threshold, routes operation to a step 130. In this case, the duration of the inactive interval is monitored from this point and compared with an interval T1. So long as the sensor output remains below the threshold, a loop comprising steps 126 128 and 130 is executed until the sensor output has been below the predetermined threshold for a time period that is greater than T1. The value that is selected for T1 will depend on the type of device as well as the environment that it is expected to occupy in use. For the purposes of illustration, but not by way of limitation, T1 could be between 50 ms and 1 second, as well as shorter or longer times if desirable. Responsive the sensor remaining sufficiently low for at least T1, step 130 then causes step 132 to resume normal operation of the drive followed by a return to start 100 in step 134. In restarting normal data access operations using hard drive 30, actuator 40 is allowed to access disk arrangement 44 and any data accesses that were paused, responsive to a triggering event, are resumed and completed. On the other hand, at any time step 128 establishes that the sensor output is greater than the predetermined threshold, step 136 then causes the actuator to remain parked and steps 126, 128 and 136 form a loop until the sensor output drops below the predetermined threshold.

Another method for protecting against time-varying magnetic fields is to record and analyze the magnetic field over time. By fitting the measured values to a variety of probable curves (sinusoidal, linear, square wave, exponential, logarithmic), it is possible to predict the future value of the external magnetic field at any given time. The drive can then anticipate that the threshold may shortly be exceeded again and remain in the parked state.

With respect to the selection of the predetermined threshold or other thresholds yet to be described, it should be appreciated that, if the external field is very weak, it will cause no significant degradation to magnetically stored information in the drive. Fields produced by a disk drive motor itself are in this category. This level of magnetic field strength will be referred to as having an upper intensity value of M1.

If the field is of greater magnitude than M1, then there might only be a temporary degradation in performance, such as reduced data transfer rate because of errors and retries in reading the data from the disk. In this case, the performance degradation will be alleviated once the stray field reduces. In other words, there is no permanent damage to the disk drive or data stored therein such that these errors may be termed as “soft errors.” This level of stray magnetic field strength will be referred to as occurring in a range having a lower limit of M1 and having an upper limit of M2. Accordingly, only soft errors should occur in the range that is between M1 and M2. Hence, this range may be referred to as a “soft error” range.

For still higher fields above M2, the disk drive may experience severe difficulty in reading data from the disk (or severe difficulty in writing to the disk, if a write operation is requested by a host device)—severe to the point where the read and/or write operations may fail and result in errors reported to the host. In this moderate case, the errors/problems will also be alleviated once the stray field reduces. Again, there is generally no permanent damage to the disk drive. In this same case, however, is also possible that the servo information stored on the disk and which is read used for use in tracking so as to provide controlled movement of the transducer(s) or head(s) which access the storage media, will also be difficult to read accurately. In this case, the drive control circuitry can lose control of the head position, allowing the control system to seek rapidly and in an uncontrolled manner by moving the heads back and forth across the disk. In an effort to recalibrate the servo, the control circuitry may cause the heads to repeatedly load onto and unload off the disk, for example, to and from a ramp that is located adjacent to the rotating disk. Both the rapid uncontrolled seeks and the frequent load/unload commands have the potential to cause damage to the drive. Accordingly, it is desirous to avoid this mode of operation. Therefore, attempting to perform a read operation in this magnetic environment could pose a risk in creating what are termed to be “hard errors.” This level of field strength will be indicted as having an upper limit of M3 such that a range from M2 to M3 characterizes this behavior.

In even higher fields (i.e., above M3), the disk drive will continue to experience severe difficulty in reading data from the disk (or severe difficulty in writing to the disk if a write operation is requested by the host) severe to the point where the read or write operations will fail and result in errors reported to the host. In this case, while these operations are being attempted, certain data on the disk will become damaged and lost due to magnetic erasure as a result of the aforedescribed focusing effect. The damaged data can be “user data” in the sense of data sectors normally written/read by the host system, but the damaged data can also be the highly critical servo data. Loss of the servo data can result in catastrophic failure of the disk drive. Loss of enough user data can also result in catastrophic failure of the host system. In this severe case, the damage is permanent and the functional problems will persist even after the stray field reduces. In addition, the magnetic field can cause changes in the speed of the motor rotation, which can lead to sudden reductions in the flying height of the head. This reduction can cause the head to come into contact with the disk, which often produces a data loss or even a catastrophic failure of the drive. This level of field strength is designated as having an upper limit of M4 such that a range from M3 to M4 characterizes this behavior.

In cases with extremely high fields, above M4, the field itself is so high that certain data on the disk will become damaged and lost due to magnetic erasure by the stray magnetic field itself, even if the drive is not in operation. In addition, it is known that these fields can hasten the thermal decay of the data stored on the drive. The damaged data could be “user data” in the sense of data sectors normally written/read by the host system, but the damaged data could also be the highly critical servo data. Loss of the servo data could result in catastrophic failure of the disk drive. Loss of enough user data could also result in catastrophic failure of the host system. In this severe case, the damage is permanent and the functional problems will persist even after the stray field reduces. In this case, if the heads are already parked, an additional action can include informing the user to remove the drive from the field.

It should also be appreciated that the orientation of the magnetic field is a concern. For example, while not intending to be bound by theory, it is thought that, in the field focusing effect regime, an applied field oriented perpendicular to the plane of the disk is more likely to be focused in a deleterious way than is a field oriented in the plane of the disk. Similarly, while not intending to be bound by theory, it is expected that, for longitudinal recording, an applied, stray field oriented in the plane of the disk is more likely to be deleterious than one oriented perpendicular to the disk. Conversely, for perpendicular recording, an applied, stray field oriented perpendicular to the disk is more likely to be deleterious than one oriented in the plane of the disk. Thus, reflexive actions and user notifications may also be based no only on the intensity of a stray field, but its orientation in conjunction with the intensity.

It should be specifically understood and appreciated that every device that is sensitive to external fields will have its own distinct levels of protection required. The recommended method for determining these levels is experimentation with the actual device in its host environment as well as theoretical considerations such as, in the hard drive case, the disk coercivity. In one embodiment, a 3D Helmholz coil arrangement, capable of achieving 3000 Oe fields in any direction, could be used to determine the various thresholds at which damage begins. In another embodiment, a strong permanent magnet could be brought into proximity of the device and the fields and orientation determined by measurement.

For the example of a hard drive, it should also be appreciated that each head and media design, as well as new methods of recording the information (e.g. perpendicular recording vs. longitudinal recording) will change the sensitivity of any given device. For example, it has been observed in the past that perpendicular recording heads are particularly sensitive to external magnetic fields.

By of example, suitable limits for a particular hard drive such as the CORNICE.™ 4.0 G drive, may be set as described in Table 1.

TABLE 1 Threshold Magnetic Field Limits Threshold Magnitude Orientation M1  10 Oe Any M2 100 Oe Any M3 300 Oe Any M4 3500 Oe  Any

It should be appreciated that this Table 1 could set forth different values for different orientations. For purposes of margin of error for a portable device wherein the orientation of the device may change abruptly, however, the thresholds can be defined without respect to orientation.

Based on the various levels of stray magnetic field strength, described immediately above, another embodiment of sensor code is illustrated in FIG. 3, generally indicated by the reference number 92′. This code begins at start 200 and, thereafter, performs a sensor read at 202. Step 204 then compares the obtained sensor reading to threshold M2, above which hard errors are potentially created. If the value is greater than M2, step 206 causes the drive actuator to park or remain parked. A new sensor reading is then obtained by repeating step 202. On the other hand, if the value obtained in step 202 is less than M2, step 208 compares the reading with threshold M1. In this regard, soft errors occur between threshold M1 and threshold M2. Accordingly, if the sensor reading is below M1, normal operation continues at step 210 and, thereafter, returns to start 200.

One concern resides in the possibility that magnetic sensor 80 could be defective by continuously, falsely indicating an external magnetic field state. Accordingly, if the sensor reading is greater than M1, step 226 uses the actuator to attempt a data read from the disk. At 228, a decision is made based on whether errors occurred during the attempted data read. If one or more errors were detected, step 230 parks the actuator or causes the actuator to remain parked and then refers operation to start 200. If no errors were detected at 228, it is assumed that the magnetic sensor is defective and step 232 causes the sensor code to be disabled and may issue a warning 240 to the user on display 17 of FIG. 1 to have the device serviced. Normal operation can then resume without monitoring the magnetic sensor. In this way, host device functionality can be maintained, although at the expense of reduced protection from external magnetic field events. This testing operation is not performed with respect to exceeding threshold M2, due to the possibility that the device is indeed in a continuous magnetic field and risk of operation while the magnitude of the field exceeds M2 may be unacceptable. In this regard, the host device may issue a different warning on display 17 to the user, for example, warning the user to remove the device from the external magnetic field.

Referring briefly to FIG. 1, while magnetic sensor 80 is illustrated as forming part of hard disk drive 30, it should be appreciated that this is not a requirement. For example, the magnetic sensor can be installed in the host device, as shown in phantom and indicated by the reference number 80′. In this instance, the sensor code can be executed by either host processor 12 or drive processor 50. U.S. patent application Ser. No. 11/327,569 entitled HARD DISK DRIVE WITH EXTERNAL SENSOR INTERFACE, SYSTEM FOR USE THEREOF AND METHOD, filed contemporaneously herewith and incorporated herein by reference in its entirety, illustrates the use of a magnetic sensor that is installed in the host device.

While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope. 

1. A disk drive configured to interface with a host device comprising: a magnetic medium for storing information; an actuator arrangement including at least one head for performing data access by moving the at least one head proximate to the magnetic medium; and a stray magnetic field protection arrangement configured to detect a stray magnetic field to which the disk drive is exposed, the stray magnetic field protection arrangement further configured to cause the actuator arrangement to park the at least one head if a read operation following measurement of the stray magnetic field having a magnitude greater than a first threshold results in an error.
 2. The disk drive of claim 1, wherein the stray magnetic field protection arrangement is further configured to cause the actuator arrangement to park the at least one head following detection of the stray magnetic field having at least a second threshold magnetic field intensity and wherein the stray magnetic field protection arrangement causes the actuator arrangement to cause the at least one head to remain parked following detection of the stray magnetic field having the second threshold magnetic field intensity so long as the stray magnetic field is greater than the second threshold magnetic field intensity.
 3. The disk drive of claim 1, wherein the stray magnetic field protection arrangement forms a portion of the disk drive.
 4. The disk drive of claim 1, wherein the stray magnetic field protection arrangement includes a magnetic field sensor.
 5. The disk drive of claim 1, wherein the stray magnetic field protection arrangement is configured to confirm operation of the magnetic field sensor based on detecting at least one read error in association with the read operation.
 6. The disk drive of claim 5, wherein the stray magnetic field detection arrangement is configured to disable the magnetic field sensor based on an absence of at least one read error in association with the read operation.
 7. The disk drive of claim 1, wherein the stray magnetic field protection arrangement includes a magnetic field sensor that is located in the disk drive.
 8. The disk drive of claim 1, wherein the stray magnetic field protection arrangement includes a magnetic sensor that is selected from the group consisting of Hall effect sensors, magnetoresistive, magneto-impedance sensors, magneto-optic sensors, search coil, flux-gate magnetometers, Superconducting Quantum Interference Devices, spin-resonance magnetometers, magneto-biological sensors, photon precession sensors and nuclear precession sensors.
 9. The disk drive of claim 1 wherein the stray magnetic field protection arrangement includes a sensor arrangement having a tri-axial response.
 10. The disk drive of claim 1 wherein the first threshold magnetic field intensity corresponds to a magnitude of the stray magnetic field that induces an operational instability in the operation of the disk drive generally without producing corruption of information that is stored on the magnetic medium.
 11. A method for operating a memory device having a magnetic medium storing information and means for accessing the magnetic medium comprising: detecting a stray magnetic field to which the memory device is exposed; performing a read operation following measurement of the stray magnetic field having a magnitude greater than a first threshold; and disabling read and write operations if the read operation results in an error.
 12. The method of claim 11, further comprising performing the test read only if the stray magnetic field is less than a second threshold greater than the first threshold.
 13. A disk drive configured to interface with a host device comprising: a magnetic medium for storing information; an actuator arrangement including at least one head for performing data access by moving the at least one head proximate to the magnetic medium; and a stray magnetic field protection arrangement supported by at least a selected one of the disk drive and the host device, the stray magnetic field protection arrangement including a magnetic field sensor for detecting a stray magnetic field to which the disk drive is exposed, wherein the stray magnetic field protection arrangement is configured to output an indicator that the magnetic field sensor is faulty if a read operation following measurement of the stray magnetic field having a magnitude greater than a first threshold does not result in an error.
 14. The disk drive of claim 13, wherein the stray magnetic field protection arrangement includes a magnetic field sensor that is located in the disk drive.
 15. The disk drive of claim 13, wherein the stray magnetic field protection arrangement includes a magnetic sensor that is selected from the group consisting of Hall effect sensors, magnetoresistive, magneto-impedance sensors, magneto-optic sensors, search coil, flux-gate magnetometers, Superconducting Quantum Interference Devices, spin-resonance magnetometers, magneto-biological sensors, photon precession sensors and nuclear precession sensors.
 16. A device comprising: a magnetic storage element; means for reading from and writing to the storage element; and a stray magnetic field protection arrangement configured for detecting a stray magnetic field to which the magnetic storage element is exposed, wherein the stray magnetic field protection arrangement is configured to disable reading from and writing to the magnetic storage element if a test read following measurement of the stray magnetic field having a magnitude greater than a first threshold results in an error.
 17. The device of claim 16, wherein the stray magnetic field protection arrangement is further configured to perform the test read only so long as the stray magnetic field is less than a second threshold greater than the first threshold.
 18. The device of claim 16, wherein magnetic storage element is a magnetic disk.
 19. The device of claim 16, wherein the stray magnetic field protection arrangement includes a magnetic field sensor.
 20. The device of claim 19, wherein the stray magnetic field protection arrangement is configured to confirm operation of the magnetic field sensor based on detecting at least one read error in association with the test read.
 21. The device of claim 16, wherein the stray magnetic field protection arrangement includes a magnetic sensor that is selected from the group consisting of Hall effect sensors, magnetoresistive, magneto-impedance sensors, magneto-optic sensors, search coil, flux-gate magnetometers, Superconducting Quantum Interference Devices, spin-resonance magnetometers, magneto-biological sensors, photon precession sensors and nuclear precession sensors.
 22. The device of claim 16, wherein the stray magnetic field protection arrangement includes a sensor arrangement having a tri-axial response. 